1. Field of the Invention:
The present invention is related to a method of forming a dielectric of the type used in semiconductor damascene applications, and more particularly to an improved process for forming a low-dielectric-constant interface layer having improved characteristics.
2. Description of the Background:
Manufacturers of integrated circuits (ICs) continue to make ever-smaller devices, which allow for greater speed, but require increased device packing densities. T he resulting increase in packing densities on a semiconductor chip, and the associated increase in functionality and complexity, require features which are smaller, more complex, and more closely-spaced.
As IC feature sizes are made smaller, for example to 0.25 microns and below, problems, such as misaligned or "unlanded" vias, increased resistance, and resistance-capacitance (RC) coupling, seem unavoidable. For example, as features become small and more closely-spaced, RC delays become an increasing part of total signal delays, offsetting any speed advantage derived from the smaller device size. RC delays thus limit improvement in device performance. One way to improve device performance and reliability would be to lower the resistivity using highly conductive metals, such as copper. Of importance to the present invention is the improvement of device performance and reliability by way of reducing capacitance, for example, by employing lower dielectric constant (low-k) materials.
Since capacitance is directly proportional to the dielectric constant (k), RC problems in ICs, can be reduced if a low-dielectric-constant material is used as the insulating material. The need for lower dielectric constant materials for use as intermetal and interlevel dielectrics for modern semiconductor technology is well known in the semiconductor industry. For example, silicon dioxide (SiO.sub.2), has long been used as a dielectric for integrated circuits because of its excellent thermal stability and relatively good dielectric properties (k.about.4.0). However, the need exists for a dielectric material which is suitable for use in ICs which has a lower dielectric constant than SiO.sub.2. After extensive study, a very promising dielectric material has been identified, known as Fluorosilicate Glass (FSG), which has a dielectric constant (k) of less than 3.7.
Many processes are known for depositing FSG thin film layers for damascene applications. One of the most important advantages of FSG is the simplicity with which it may be deposited, especially with CVD processes. As shown in FIG. 1, the process 10 begins with the in-situ deposition 12 of the reactants in a reaction deposition chamber. After an optional, yet, conventional SiN deposition 14, the reactant gas, containing reactants, such as N.sub.2 O, SiF.sub.4 and SiH.sub.4, are introduced into the chamber through an inlet port and arc excited to create ions or radicals by a high electric field created by an RF voltage. The electric field causes the inlet gas to become excited enough to form a glow discharge or plasma. When a plasma is used to generate the ions or radicals that recombine to give the desired film, the process is plasma-enhanced (PECVD). Plasma enhanced deposition 16 occurs when the molecules of the incoming gases are broken up in the plasma and the appropriate ions are recombined on the substrate surfaces to give the desired FSG film.
Next, an optional hardmask deposition 18 is applied to the structure, which is subsequently etched 20, or similarly cut, to create the desired pattern required for semiconductor applications. At this stage in the conventional process, a layered structure 30, similar to that shown in FIGS. 2A or 2B, has been developed. Next, the structure is degassed 22 and a metal barrier layer is deposited 22 followed by metal deposition 24, planarization 26, and final clean 28. Unfortunately, the structure formed using the conventional technique 10, is subject to many drawbacks. Generally, the degassing 22 typically fails to remove free fluorine ions which are a by-product in the film of the PECVD process. The film in this stage is considered chemically unstable. Moreover, FSG film tends to absorb H.sub.2 O. The presence of free fluorine ions and hydrogen may lead to the eventual formation of HF gas, which tends to degrade adhesion properties of the FSG. For example, after the application of the metal barrier layer, any HF gas that may form may not be able to diffuse out, which usually leads to blistering and bubbling of the metal and etch stop layers. Moreover, most methods used for FSG film deposition are not practical to use because of their unstable or higher cost of ownership (CoO).
For these reasons, what is needed is an improved process for depositing a robust FSG film on a substrate, metal barrier, or etch stop layer, such that the FSG film exhibits, for example, improved chemical stability, deposition rate, uniformity of thickness, and adhesion characteristics.